Lead is the most common component in pistol bullets, given its high density, plasticity and low cost. However, its high toxicity both for the environment and for the person firing the bullet, together with its tendency to generate fumes and small particles during shooting has originated the search for more ecological alternatives that maintain the low cost.
During shooting exercises there is a potential risk of being wounded by ricocheting bullets. When the bullet impacts on a surface with a certain angle there is the possibility that not all of the kinetic energy it carries dissipates by breaking or deforming the bullet, that is, part of this energy may remain in the deformed bullet or in a fragment of the bullet, possibly causing undesired injury or collateral damage to other people or objects.
This effect may be avoided or minimised by making the bullet more “frangible”, that is, by making it easier for the bullet to break into small parts when it impacts on its main target, such that the energy associated to these tiny fractions of the bullet is very small and the collateral damage they may cause is minimal.
Methods have been developed in the prior art to manufacture frangible bullets by pressing and heat treating stainless steel or other partially alloyed steels with copper base materials.
Most known processes are based on the use of a metal “adhesive” that melts at low temperatures and distributes itself within the base material matrix by capillarity. In the case of copper based materials, the system is supplemented with the formation of superficial Cu—Sn intermetallic bonds that both facilitate the resistance of the material when “sheathed” inside the cartridge and ensure frangibility when fired.
One example of a material and process for the manufacture of frangible bullets is found in U.S. Pat. No. 6,074,454, which uses a copper-based powder that is pressed and then sintered, where the sintering is performed at high temperature, usually within the range of 815.6° C. to 1037.8° C. (1500 to 1900° F.).
U.S. Pat. No. 6,536,352 describes the powder of a matrix metal with a high melting point and a metal powder with a melting point substantially below that of the matrix metal, in short, the teachings of this document require two metal powders of different characteristics.
Another document of the prior art is U.S. Pat. No. 6,090,178, where the bullet is made of a plurality of metal particles and a binder that breaks easily, consisting essentially in an intermetallic that can be a metal or metalloid such as tin, zinc, gallium, silicon, arsenic or aluminium, for example. Once again, two different metallic materials are used to manufacture the bullet.
Similarly, U.S. Pat. No. 6,263,798 describes a cartridge where the bullet is formed by a plurality of metal particles consisting of unsintered copper and tin that are bound to one another using a binder that breaks easily, consisting essentially of an intermetallic compound of copper and tin.
Other documents of the prior art relating to compositions for bullets are described in U.S. Pat. No. 5,399,187 and U.S. Pat. No. 5,760,331, where the composition includes tungsten W. Additional compositions are also described in U.S. Pat. No. 5,894,644; U.S. Pat. No. 6,551,375; and U.S. Pat. No. 5,950,064, where the composition of the bullet is based on FeW with different additions of W and even Portland cement.
Even U.S. Pat. No. 6,569,381; U.S. Pat. No. 6,815,060; U.S. Pat. No. 6,016,754; and U.S. Pat. No. 6,439,124 describe bullets manufactured from compositions having W—Sn with or without a sheathe or jacket.
U.S. Pat. No. 5,237,930 describes a very fine powder using non-coarse copper and a thermoplastic resin such as Nylon 11 or 12 (Polyamide) and with densities of about 5.7 g/cm3 as materials to manufacture frangible bullets.
Similarly, U.S. Pat. No. 7,353,756; discloses a polyether binder in 30-40% by weight with low density for frangible bullets. U.S. Pat. No. 5,442,939 discloses another composition using stainless steel with Fe and with 2% of graphite to help break the ammunition. U.S. Pat. No. 5,950,064 proposes liquid phase sintering to gain density using FeW—Fe—Zn.
As can be observed, technologies exist for the manufacture of frangible bullets, but there is still the need for new compositions and methods that represent reliable alternatives for the manufacture of frangible bullets